1. Field of the Invention
The present invention relates generally to a method of manufacturing a circuit assembly having a circuit board with electronic components mounted on opposite sides thereof and a heat sink. More particularly, the present invention relates to a method of curing an adhesive provided between the circuit board and the heat sink by applying heat to the adhesive through the heat sink.
2. Description of Related Art
Heat sinks are often included in modern circuit assemblies to transfer heat away from board-mounted, electronic components. These circuit assemblies are often designed such that the heat sink is adhesively bonded to a side of the circuit board opposite from the side populated by the electronic components. One known method for manufacturing such an assembly includes applying an adhesive between the heat sink and the unpopulated side of the board and convection curing the adhesive in an oven.
This approach has been found to be disadvantageous for several reasons. First, board space cannot be utilized in the most effective manner by concentrating the components on a single side of the board. Second, the components and circuit board selected must be capable of withstanding exposure to the desired oven curing temperature. If the oven temperature is reduced to accommodate more temperature-sensitive components and circuit boards, the time required to cure the adhesive can increase significantly, decreasing the efficiency of the process. Even at normal oven curing temperatures, the process is relatively slow, generally requiring cycle times of about 20-40 minutes for conventional heat curable adhesives. Another problem associated with oven curing is that it is difficult to apply pressure to the adhesive during the curing cycle. As a result, it is difficult to control the thickness and quality of the adhesive bondline that joins the heat sink to the circuit board. Mechanical fasteners, such as screws, rivets and clips, have been used to compress the adhesive during oven curing, but such fasteners cannot tightly control the adhesive bondline, especially beneath the components. Moreover, such fasteners increase the overall size, weight and cost of the circuit assembly.
Given the above-described drawbacks of the prior art, it would be desirable to provide a method for manufacturing a circuit assembly that permits temperature-sensitive circuit boards having temperature-sensitive electronic components mounted on opposite sides thereof to be adhesively bonded to a heat sink without the need for an extended oven cure.
Moreover, it would be desirable to provide a method for manufacturing a circuit assembly that enables the adhesive to be cured more rapidly than in conventional oven curing processes.
It would also be desirable to provide a method for manufacturing a circuit assembly that permits a uniform adhesive bondline to be formed between the circuit board and the heat sink.